Scan samples of 2 social groups of rhesus monkeys and 2 social groups of pigtailed macaques taken from May through November of 1997 revealed differences in subgroup sizes between the two species. Scans were taken every minute for a 20-minute period on each group for a total of 132 hours of observation. Averages were computed for each observation session, and groups were compared by species and by group size. Pigtailed monkeys are more frequently found alone, or are found in groups of 5 or more. Rhesus monkeys are less frequently found alone, and usually huddle in groups of 3 to 5. There were no differences in overall affiliation between the smaller social groups (n=25) and the larger social groups (n=45). Observations were also carried out on aggression followed by reconciliation, but the sample size was too small for